1. Field of the Invention
This invention relates to a method, device and reagents for the detection of plasma lipoprotein (a). In particular, the invention relates to a test strip device for use in a competitive immunoassay for the semiquantitative measurement of plasma lipoprotein (a).
2. Description of Related Art
Lipoprotein (a) [Lp(a)] was described as a genetic variant of low density lipoprotein (LDL) in 1963 (Kaare Berg, Acta Pathol Microbiol Scand, 59:369-381; 1963). Later, Lp(a) was found to be different from LDL in terms of lipoprotein particle composition, electrophoretic mobility, particle size and buoyant density (Rider et al., Circulation, 42(13):10; 1970).
After a simple disulfide reduction, the Lp(a) particle dissociates into LDL and apolipoprotein (a) [Apo(a)] molecules. This finding led to the conclusion that the Apo(a) molecule is covalently linked to Apolipoprotein B-100 (Apo B-100) by a disulfide bond (Gaubatz et al., Journal of Biological Chemistry, 258:4582-4589, 1983; Fless et al., Journal of Biological Chemistry, 259:11470-11478; 1984; Fless et al., Journal of Biological Chemistry, 261:8712-8718; 1986).
Recently, it has been found that the Apo(a) molecule on the Lp(a) particle has a cDNA sequence similar to that of human plasminogen (Eaton et al., Proc Natl Acad Sci, 84:3224-3228, 1987; McLean et al., Nature, 330:132-137; 1987). In the study of atherosclerosis, the Lp(a) particle has been found to cause the formation of a plaque of degenerated thickened arterial intima (i.e., atheroma) to a greater degree than does LDL (Bihari-Varga et al., Arteriosclerosis, 8:851-857; 1988; Collen, D., Thromb Haemost, 43:77-89; 1980). This may be partly due to the disturbance of the balance between thrombogenesis and fibrinolysis caused by Lp(a). In addition, high levels of Lp(a) may favor atherosclerotic plaque formation by inhibiting plasminogen activation by tissue plasminogen activator (Olofson et al., Euro Heart, 10:77-82, 1989; Hamsten et al., Lancet, 2:3-8; Jul. 4, 1987).
Numerous studies have indicated that high levels of plasma Lp(a) are strongly associated with atherosclerosis (Ellefson et al., Mayo Clin Proc, 46:328-332; 1971; Berg et al., Clin Genet, 6:230-235; 1974; Avogaro et al., Clin Chem Acta, 61:239-246; 1975; Dahlen et al., Clin Genet, 9:558-566; 1976). When the plasma Lp(a) level is above 30 milligrams/deciliter, which is equivalent to 7 milligrams/deciliter of Lp(a) protein, the relative risk of coronary atherosclerosis is raised about twofold. When LDL and Lp(a) are both elevated, the relative risk is increased to the range of fivefold (Armstrong et al., Atherosclerosis, 62:249-257; 1986). It has been reported that heterozygous familial hypercholesterolemia patients with high plasma Lp(a) may have developed atherosclerosis earlier than those with low plasma Lp(a) (Utermann et al. Proc Natl Acad Sci, 86:4171-4174; 1989). While the function of Lp(a) is unknown, a significant correlation has been established between elevated levels of plasma Lp(a) and coronary artery disease.
Lp(a) has been measured quantitatively by radioimmunoassay (Albers et al., J Lipid Res, 18:331-338; 1977), radial immunodiffusion (Albers et al., Lipid, 9:15-26; 1974), rocket immunoelectrophoresis (Gaubatz et al., Meth Enzymology, 129:167-186; 1986), and recently by enzyme-linked immunosorbent assay (Labeur et al., Clin Chem, 35(7);1380-1384; 1989; Abe et al., Clin Chem Acta, 177:31-41; 1988; Fless et al., J Lipid Res, 30:651-662; 1989). All of these previous methods have required multiple manipulations of test sample and assay reagents, complex instrumentation and/or extended time for performance. Therefore, it would be beneficial to have a rapid one-step, non-instrumented, competitive immunochromatographic method that can semiquantitatively measure plasma Lp(a) levels to facilitate the identification of individuals having an increased risk for coronary artery disease and the progression of atherosclerotic lesions.